libogc : quaternion multiplication problem (and solution)

[Minimalist]

Hello,

I think that I found a mistake in the libogc implementation of quaternions.
c_guQuatMultiply uses + instead of - several times.
Here is a working version of the function :

Code: Select all

void my_guQuatMultiply(Quaternion *a,Quaternion *b,Quaternion *ab)
{
	Quaternion *r;
	Quaternion ab_tmp;
	
	if(a==ab || b==ab) r = &ab_tmp;
	else r = ab;

	r->w = a->w*b->w - a->x*b->x - a->y*b->y - a->z*b->z;
	r->x = a->w*b->x + a->x*b->w + a->y*b->z - a->z*b->y;
	r->y = a->w*b->y + a->y*b->w + a->z*b->x - a->x*b->z;
	r->z = a->w*b->z + a->z*b->w + a->x*b->y - a->y*b->x;

	if(r==&ab_tmp) *ab = ab_tmp;
}

As a bonus, here is a fonction that converts a quaternion into a matrix :

Code: Select all

void my_guQuatToMtx(Quaternion *qua, Mtx m)
{
	m[0][0] = 1-2*qua->y*qua->y-2*qua->z*qua->z;
	m[0][1] = 2*qua->x*qua->y-2*qua->w*qua->z;
	m[0][2] = 2*qua->x*qua->z+2*qua->w*qua->y;
	m[0][3] = 0;
	m[1][0] = 2*qua->x*qua->y+2*qua->w*qua->z;
	m[1][1] = 1-2*qua->x*qua->x-2*qua->z*qua->z;
	m[1][2] = 2*qua->y*qua->z-2*qua->w*qua->x;
	m[1][3] = 0;
	m[2][0] = 2*qua->x*qua->z-2*qua->w*qua->y;
	m[2][1] = 2*qua->y*qua->z+2*qua->w*qua->x;
	m[2][2] = 1-2*qua->x*qua->x-2*qua->y*qua->y;
	m[2][3] = 0;
}

Hope it will help someone.

PS : I'm currently working on a rubik's cube homebrew for Wii, which uses quaternions to rotate. The code is quite ugly at the moment, but if you need a ready-to-compile sample, feel free to ask for it.